2. GLYCOGENOLYSIS, ANAGHA P JAYAN , ST.MARY’S COLLEGE - THRISSUR
Glycogen
Multibranched subunit of glucose.
Serve as a form of energy storage in humans, animals, fungi etc.
consist of 2 types of linkages, alfa(1 4)linear linkage alfa(1 6) branching
linkage.
Storage
Storage form of glucose in animals (animal starch).
Granular form , high in liver (6-8%) and muscles(1-2%).
3. Glycogenolysis
Breakdown of glycogen to glucose 1 phosphate and glucose in liver and
muscles.
To meet the immediate energy demands of the body or when the blood
glucose level is low.
Steps involved in glycogenolysis.
Step-1 action 0f glycogen phosphorylase.
Alpha-1,4-glycsidic bonds(from non-reducing ends)are cleaved
sequentially by enzyme glycogen phosphorylase to yield
Gluc-1-phosphate .
This proses is called phosphorolysis.
Limits : degrades the glycogen molecules until 4 glucose residues remain
on each chin before a branch point (stops at 4 glucose residue
GLYCOGENOLYSIS, ANAGHA P JAYAN , ST.MARY’S COLLEGE - THRISSUR
4. The glycogen so formed is known as limit dextrin which can not be
further degraded by phosphorylase.
Step-2 action of debranching enzyme
The branch of glycogen are cleaved by debranching enzyme(bifunctional
enzyme ) .
GLYCOGENOLYSIS, ANAGHA P JAYAN , ST.MARY’S COLLEGE - THRISSUR
5. 1. Glycosyl 4:4 transferase (oligo alpha 1,4→1,4 glucan transferase)
Activity removes a fragment of 3 or 4 glucose residues from a branch
and transfer them to another chain.
2.Amylo alpha-1,6-glucosidase
Breaks the alpha-1,6-bond at the branch with a single glucose residue.
Step-3 Formation of glucose -6-phosphate and glucose
Combined action of glycogen phosphorylase and branching enzyme free
glucose(8:1 ratio) are produced .
Glucose- 1-phosphate is converted to glucose-6-phosphate by the enzyme
phosphoglucomutase.
In liver, kidney, and intestine Glu-6-p is converted in to glucose.
GLYCOGENOLYSIS, ANAGHA P JAYAN , ST.MARY’S COLLEGE - THRISSUR
